Resolve bug in adding iterations

[ablaom]

Resolves #128

[codecov-commenter]

Codecov Report

Merging #129 (5c7a652) into dev (a5e4448) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #129   +/-   ##
=======================================
  Coverage   86.60%   86.60%           
=======================================
  Files          11       11           
  Lines         575      575           
=======================================
  Hits          498      498           
  Misses         77       77           

Impacted Files	Coverage Δ
src/tuned_models.jl	91.75% <100.00%> (ø)

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[ablaom]

Failure of CI for Julia 1.0 is a known issue tracked here and orthogonal to this important bug fix - so merging anyhow.